The OKT3 monoclonal antibody entails a transient acute nephrotoxicity when used either to prevent or to treat renal allograft rejection. This nephrotoxicity was reproduced experimentally in mice injected with 145-2C11, an anti-CD3 monoclonal antibody which shares many properties with OKT3. Both clinical and experimental data suggest that the renal lesions are due to the systemic release of cytokines that occurs prior to the immunosuppression. Pre-treatment with corticosteroids before the injection of anti-CD3 monoclonal antibody mitigates both the release of cytokines and the nephrotoxicity, in a dose-dependent manner. Experimental data suggest that very high doses of methyl-prednisolone (50 mg/kg) administered 2 to 3 hours before the monoclonal antibody are necessary to obtain an optimal protection.